In recent years, the morbidity rate of the rheumatic disease in Japan has reached to 1% of the national population, and accordingly, the rheumatic disease has been regarded as a kind of a folk disease at present. An abrasion loss at a cartilage portion (destruction of cartilage) and/or subtle changes of a bone shape and a bone trabeculae are observed as its early symptoms, and then, at the time when the symptoms have worsened, considerable changes of shape of the bone sections can be observed significantly. Accordingly, by observing the shape of cartilage portion and subtle changes of the bone shape and the bone trabeculae, it is possible to make a diagnosis with respect to the disease situation of the rheumatic disease at its early stage. Considering the actual condition that only medical treatments for stopping the progress of the symptoms are currently available as the medical treatments for the rheumatic disease, it is important to detect the rheumatic disease at its early stage and to speedily shift the patient into the phase of applying the medical treatments.
However, the above-mentioned early symptoms of the rheumatic disease have been hardly detected by observing the X-ray photographic image, which has been widely accepted as a simple and convenient inspection method, and accordingly, it has been difficult for a doctor or the like to determine whether or not the rheumatic disease has actually developed.
On the other hand, in recent years, instead of the radiographic images acquired by radiographing the patient, images acquired by employing the MRI (Magnetic Resonance Imaging) has been considered as a tool for making diagnosis, in order to detect the changes of cartilage tissues. Further, recently, in the field of the radiographic image capturing technologies, there has been reported such a technology that extracts a radiant beam, which straightly progress in parallel, so that the above-extracted radiant beam are used for capturing images of the cartilage portion concerned. However, since the patient has been heavily burdened with the MRI photographing operation from the viewpoint of the cost and time required for making a diagnosis, it has been difficult to perform the MRI photographing operation in the framework of the regular physical examination. Therefore, there has been such a problem that it has been difficult to periodically perform the MRI photographing operation so as to observe (inspect) the changes of the joint portions, such as fingers, etc., over time, as a longitudinal diagnosis.
Further, since a huge image-capturing installation is necessary for conducting the image-capturing operation that employs the radiant beam, and, sometimes, several tens of minutes are required for completing the image-capturing operation, it has been virtually impossible for a general-purpose medical facility to employ the radiant beam for conducting the image-capturing operation. Due to the present situations as aforementioned, it has been desired to make it possible to simply and easily make a diagnosis on the diseases of cartilage portion at its early stage, such as a subtle change in a shape of joint portion, a subtle change in the bone shape, a swelling, etc.
For instance, in order to make a diagnosis on the case of the rheumatic diseases at its early stage, it is indispensable to capture such a radiographic image that has a high sharpness being sufficient for recognizing a subtle change of a symptom in the patient, represented thereon. As the radiological image capturing apparatus that can capture a radiographic image having a sufficiently high sharpness, there has been well-known the technology for capturing a phase contrast image by employing the radiological image capturing apparatus, for instance, set forth in Patent Document 1. According to the technology set forth in Patent Document 1, even for such a subject whose X-ray absorbing rate is specifically lower than other subjects to such an extent that its radiological image having a sufficient contrast cannot be formed by employing the normal X-ray absorbing action, it has been possible to obtain such an radiological image in which contrast of the peripheral portions (edge portions) are specifically emphasized. Further, it has bee possible to apply the abovementioned technology not only to joint disorders, which are represented by the rheumatic disease, but also to various kinds of sections, such as a breast image capturing operation that should be capable of detecting a micro calcification from a breast, most of which is formed by a soft tissue, an operation for radiographing a child body, almost bones of which are cartilages, etc.
Further, as the technology for further emphasizing the contrast of the peripheral portions of the subject, for instance, Patent Document 2 sets forth an X ray radiographing apparatus employing the Talbot interferometer method based on the Talbot effect caused by the diffraction grating. Still further, Non-patent Document 1 sets forth an X ray radiographing method employing the Talbot-Lau interferometer method, which is improved from the Talbot interferometer method.
[Patent Document 1] Tokkai 2004-248699 (Japanese Laid-open Non-Examined Patent Publication)
[Patent Document 2] WO 2004-058070 (International Publication)
[Non-patent Document 1] “recent development of X ray phase imaging” written by Atsushi Momose, Medical Imaging Technology, Japanese Society of Medical Imaging Technology, November, 2006, vol. 24, No. 5, page 359-366
However, since the radiant beam X ray source, which requires a special facility, is employed in the Talbot interferometer method set forth in Patent Document 2, there has been a problem that it is virtually impossible for general-purpose medical facilities, widely exiting in the society, to employ the Talbot interferometer method. In addition, in such the general-purpose medical facilities, it has been assumed that low energy X rays are to be irradiated onto the subject. This is because, the phase contrast effect, acquired by employing the low energy X rays, is relatively great, and the absorbing contrast effect, acquired by employing the conventional X rays radiological imaging, is relatively strong. However, since the excessively low energy X-rays tend to be absorbed into the human body, and accordingly, since an amount of the X rays arriving at a detector is relatively small, it is necessary to increase the dose of radiation exposure in order to acquire an appropriate S/N (Signal to Noise) ratio at the detector, resulting in an increase of the X-ray exposure. Further, the increase of the X-ray exposure will cause an extension of the image capturing time interval. However, it is difficult to make the movement of the human body, serving as the subject, freeze for a long time during the image capturing time interval. Then, as a result of the movements of the subject during the radiographing, an X-ray image in which the peripheral sections of the subject are blurred would be captured, and accordingly, an advantageous characteristic of the Talbot-Lau interferometer that can emphasize the contrast of peripheral sections of the subject would be deteriorated.
On the other hand, if the energy of the X rays to be irradiated onto the human body is excessively high, it has been acquired such a knowledge that an image contrast being sufficient for depicting bone tissues and soft tissues that constitute the human body cannot be obtained. Accordingly, there has been a problem that an X ray image, which is sufficiently usable for making a diagnosis on the human body, serving as the subject, cannot be obtained, unless the contrast in the X ray image can be obtained.
As abovementioned, when the radiological image capturing apparatus in conformity with the Talbot interferometer method is employed for the medical purpose, a usable range of the X ray radiation energy (precisely speaking, average energy) is relatively narrow. In addition, in order to generate the Talbot effect so as to realize the Talbot interferometer method, various kinds of strict limitations are applied to a distance between a first diffraction grating and a second diffraction grating, an interval (grating period) between diffraction elements constituting the each of the diffraction gratings, etc., as detailed later. Therefore, in order to apply the Talbot interferometer method to an operation for radiographing the various kinds of sections in the human body, specifically for such the sections that are hardly captured by the X-ray image capturing method, such as the cartilage tissue, etc., the radiological image capturing apparatus should be configured so as to fulfill the extremely strict conditions.
Further, according to the Talbot-Lau interferometer method set forth in Non-patent Document 1, a multi-slit element is disposed between the X ray source to be employed in the Talbot interferometer method and the subject. Since the X ray emitting source is converted to multi (plural) radiant sources by employing the multi-slit element, it is possible to effectively utilize the Talbot effect, even if the X ray tube having a large focal diameter is employed in the apparatus. However, the structure and configuration of the concerned apparatus become more complicated than ever, and, further, since various kinds of conditions, such as positional relationships between the multi-slit element and the other elements, etc., are added as new limitations for configuring the apparatus, the structural conditions for the concerned apparatus become still more stricter than ever, and it is required for the concerned apparatus to fulfill such the extremely strict conditions.
On the other hand, a dose of X rays, to be irradiated onto the subject by the radiological image capturing apparatus employing the Talbot interferometer method, is relatively small, compared to that to be irradiated by the other radiological image capturing apparatus employing the Talbot-Lau interferometer method. However, since the X rays are irradiated by a single X-ray emitting source, the radiological image capturing apparatus employing the Talbot interferometer method has such the advantage that a very clear X-ray image, sharpness of which is very high, can be obtained. Whereas, since the X ray emitting source is converted to the multi (plural) radiant sources by employing the multi-slit element, the Talbot-Lau interferometer method is inferior to the Talbot interferometer method in sharpness of the reproduced X ray image to some extent. However, since it is possible in the Talbot-Lau interferometer method to irradiate relatively high energy X rays onto the subject, compared to the Talbot interferometer method, the radiological image capturing apparatus employing the Talbot-Lau interferometer method has such the advantage that the X-ray radiographing operation can be completed within a shorter time than ever.
Further, if a single radiological image capturing apparatus is so constituted that the abovementioned two methods are provided within the single apparatus so as to make it possible to selectively change them to each other, for instance, by selecting one of the methods corresponding to the current purpose of capturing the X-ray image, it becomes possible to obtain the X-ray image to which the advantage of the selected method is fully applied, resulting in a very convenient apparatus. Still further, if the apparatus concerned is constituted as abovementioned, it becomes possible to appropriately make a diagnosis by adaptively selecting either the Talbot interferometer method or the Talbot-Lau interferometer method.
As aforementioned, it has been desired that the Talbot interferometer method or the Talbot-Lau interferometer method is employed for operations not only for capturing X-ray images of the joint disorders, which are represented by the rheumatic disease, but also for capturing X-ray images of various kinds of sections in human body, such as the breast image capturing operation that should be capable of detecting the micro calcification from the breast, most of which is formed by the soft tissue, an operation for radiographing the child body, almost bones of which are cartilages, etc. However, in order to achieve the abovementioned goals, it is indispensable to configure the apparatus so as to fulfill such the extremely strict conditions as aforementioned.